This invention relates generally to controlled distribution of a pressurised fluid from a fluid source and, in particular, to a device for distributing pressurised gas to selected ones of an array of delivery outlets or ports. The device is applicable for use in pressure thermoforming machinery for supplying forming air to delivery ports communicating with mould cavities during thermoformation of plastic film into thin-walled products. It will be convenient to hereinafter disclose the invention in relation to that exemplary application, although it is to be appreciated that the invention is not limited thereto.
One type of pressure thermoforming machinery includes a die body having one or more mould cavities in which thin plastic film is pressure formed into the shape of the cavities to form thin walled products such as trays and other industrial packaging items. The die body may incorporate trimming knives extending about the mould cavities for cutting the moulded trays from the plastic film. The equipment also includes a heated cutting platten arranged in a facing relationship with openings of the mould cavities in the die body, and the die body and cutting platten are relatively movable toward and away from one another. The plastic film is transported in successive steps along a path between the die body and cutting platten during operating cycles of the machinery.
In each operating cycle, the die body and cutting platten are relatively moved toward one another until a section of film is trapped between the cutting platten and trimming knives so as to create a seal therebetween. Compressed air is injected into the mould cavities forcing the film into direct contact with the cutting platten. The cutting platten is heated so as to heat soften the film section. Pressurised forming air is then introduced through small delivery ports in the cutting platten whereby the heated film is rapidly blown into the mould cavities to adopt the shape thereof.
The now formed portions of the film are cooled and the forming air vented from the cavities. The die body and cutting platten are then again relatively moved toward one another so that the trimming knives cut entirely through the film section to separate the formed products from the film.
The die body and cutting platten are then moved apart, and compressed air is forced between the formed products and the mould cavities to eject the products therefrom. As the products clear the cavities, the film is transported forward along the path carrying the formed and trimmed products clear of the die body and cutting platten, and introducing a sequential section of film to commence a new cycle.
In this type of machinery, the cutting platten has a regular close array, such as rows and ranks, of small delivery ports opening onto its cutting surface. This arrangement enables the cutting platten to be used with die bodies having differently shaped cavities, since at least some of the ports will communicate with the mould cavities when the die body and cutting platten are brought together. Accordingly, it is not necessary to change the cutting platten with each shape of mould cavity.
Various systems have been developed to control distribution of air to selected delivery ports so that only those ports communicating with the cavities are supplied with air. Those distribution systems seek to avoid air streams acting on the film outside the cavities causing uncontrolled shaping of the heated film and leading to distortion of the film and possibly misshaping of the products. Control of the airflow also ensures more efficient use of the air source, thereby reducing the required capacity of the air supply equipment.
One air distribution system provides a supply block having a series of supply channels. The cutting platten is mounted on the supply block, so that each supply channel is in communication with some of the delivery ports, and connected to the air supply through a valve control facility. The supply channels have been arranged in various patterns in an effort to increase the possible combinations of delivery ports to which air can be supplied, and thus improve the overall versatility of the thermoforming machinery. In one pattern, the channels are endless and arranged concentric with one another. In operation, air can be supplied to one or more of the supply channels through the control valve facility, and thus the delivery outlets in communication therewith.
This air distribution system enables more precise delivery of forming air to the delivery ports. However, depending on the shape of the mould cavity openings, air is still delivered to ports which are not in communication with the cavities. To that extent, the above problem with inaccurately delivered air persists. In addition, an extensive control valve facility with associated piping is required to control flow of air to the delivery ports.
A modification of this system involves provision of a distribution foil sheet interposed between the supply block and cutting platten. That sheet has flow holes therethrough arranged so as to communicate between one or more of the supply channels and only those delivery ports which will be in communication with the mould cavities during operation of the machinery. Thus, the holes in the foil sheet can act to supply air quite precisely to individual delivery ports, ensuring that air is confined to the mould cavities. Conveniently, the holes in the sheet will extend over areas which will mirror the xe2x80x9cfootprintxe2x80x9d of the openings of the mould cavities.
Although the use of this foil sheet permits precise delivery of forming air to the cavities, a disadvantage is that the foil sheet is required to be changed with each change in the shape of mould cavity openings. This necessary change over procedure is slow and heavy work because of the need to remove the cutting platten from the machinery in order to access the foil sheet. As a result, there is a significant loss of machinery production time.
An object of the present invention is to provide a fluid distribution device enabling improved fluid delivery to selected delivery ports, such as those of a cutting platten of pressure thermoforming machinery.
Another object of the present invention is to provide an improved apparatus for supplying pressurised forming gas, such as air, to a mould cavity in a die body of pressure thermoforming machinery.
With those objects in mind, the present invention provides in one aspect a fluid distribution device including:
a distribution block having an array of fluid flow passages, the flow passages being arranged in a plurality of at least first and second groups with each flow passage being included in a respective first group and a respective second group of flow passages; and,
valve means operable for controlling fluid flow through the passages, the valve means including an at least first series of valve members of which each valve member is associated with a respective one of the first group of flow passages and an at least second series of valve members of which each valve member is associated with a respective one of the second group of flow passages, each valve member being movable between a closed position preventing flow through the associated flow passages and an open position permitting flow along those passages, whereby when all of the valve members associated with any one flow passage are in the open position fluid is able to flow through that passage.
Preferably, the first groups of flow passages comprise lines of flow passages. The second groups of flow passages preferably also comprise lines of flow passages.
In one preferred form, the first groups of flow passages comprise parallel straight lines of flow passages and the second groups of flow passages comprise parallel straight lines of flow passages. The lines of flow passages of the first and second groups can extend at an angle, such as perpendicular, to one another in this form. The flow passages may be arranged in rows and ranks. With this arrangement, each row forms a respective group of flow passages in the plurality of first groups of flow passages and each rank forms a respective group of flow passages in the plurality of second groups of flow passages.
Preferably, each valve member has a separate fluid flow path therethrough for association with a respective flow passage of the respective group of flow passages. The valve member is movable so as to align and misalign all of its flow paths simultaneously with the respective flow passages to respectively permit and prevent fluid flow through the flow paths and along the flow passages. Each valve member preferably has flow apertures therethrough defining the fluid flow paths.
Preferably, each valve member is mounted in a bore in the distribution block for movement in the bore between the open and closed positions. Preferably, each bore extends along a respective row or rank of flow passages and passes through each flow passage of that row or rank. Each valve member is mounted in a respective bore so that in the closed position fluid flow through all of the flow passages of the row or rank along which the bore extends is prevented, and in the open position fluid flow along all of the flow passages is permitted.
In one preferred form, each flow passage has two bores passing therethrough, so that when the two valve members mounted in the respective bores are both in the open position, fluid is able to flow through that passage. The bores passing through each flow passage are spaced from one another in a direction along the flow passage so as to not intersect with one another.
In one preferred form, each valve member includes a valve rod extending along the respective bore. Those rods are mounted for longitudinally sliding movement along the bore between the open and closed positions, in this form. The bores and valve rods are of the same, for example rectangular or circular, cross-sectional shape.
Preferably, sealing elements are provided for fluid sealing between the distribution block and the valve members to seal against leakage of fluid from the flow passages along the bores. Those sealing elements are preferably sealingly mounted in the distribution block. Each sealing element extends about a periphery of a respective flow passage adjacent a respective bore and sealingly engages with the valve member in the bore. Preferably, a pair of sealing elements are associated with each intersection between the bores and flow passages. Each pair of sealing elements extends about the flow passage one on each side of the intersection.
In one preferred form, each sealing element is a sealing O-ring. The distribution block, in this form, includes mounting recesses extending about the flow passages and opening in to the bores for receiving the O-rings therein.
The present invention, in another aspect, provides apparatus for distributing pressurised gas from a gas source to a mould cavity in a die body of pressure thermoforming machinery, including the above fluid distribution device.
Preferably, the apparatus also includes a gas supply block having a gas distribution surface with a series of distribution channels on the surface connectable to a source of pressurised gas for distribution over the surface. The distribution block is mounted on the gas supply block so that the distribution channels are in gas communication with one end of the flow passages.
Preferably, the distribution block has a lower surface onto which each of the flow passages opens. The distribution block is mounted on the gas supply block with the lower surface in sealing face-to-face engagement with the gas distribution surface so that the distribution channels are in gas communication with the ends of the flow passages opening onto the lower surface.
Preferably, the apparatus further includes a cutting platten having a cutting surface for exposure to a mould cavity, and an array of gas delivery ports opening onto the cutting surface for flow of gas through the ports into the mould cavity during use of the apparatus. The cutting platten is mounted on the fluid distribution device so that the flow passages are in gas communication with the delivery ports.
Preferably, the cutting platten has a lower bearing surface from which the delivery ports extend to the cutting surface. The distribution block has an upper surface onto which each of the flow passages opens, and the cutting platten is mounted on the distribution block with the bearing surface in sealing face-to-face engagement with the lower surface so that each flow passage is in gas communication with at least one of the delivery ports.
The following description refers to a preferred embodiment of the fluid distribution device of the present invention. To facilitate an understanding of the invention, reference is made in the description to the accompanying drawings where the device is illustrated in that preferred embodiment. It is to be understood that the device is not limited to the preferred embodiment as hereinafter described and as illustrated in the drawings.